The invention herein described relates generally to cushioning conversion machines and more particularly to improvements in controlling the tension of the stock material fed into such machines for conversion into a dunnage product.
In the process of shipping an item from one location to another, protective packaging material is often placed in the shipping container to fill any voids and/or to cushion the item during the shipping process. Some commonly used protective packaging materials are plastic foam peanuts and plastic bubble pack. While these conventional plastic materials seem to perform adequately as cushioning products, they are not without disadvantages. Perhaps the most serious drawback of plastic bubble wrap and plastic foam peanuts is their affect on our environment. Quite simply, these plastic packaging materials are not biodegradable, and therefore they cannot avoid further multiplying our planet""s already critical waste disposal problems. The non-biodegradability of these packaging materials has become increasingly important in light of many industries adopting more progressive policies in terms of environmental responsibility.
The foregoing and other disadvantages of conventional plastic packaging materials have made paper protective packaging material a popular alternative. Paper is biodegradable, recyclable and composed of a renewable resource, making it an environmentally responsible choice for conscientious shippers.
While paper in sheet form could possibly be used as a protective packaging material, it is usually preferable to convert the sheets of paper into a relatively low density pad-like cushioning or dunnage product. This conversion may be accomplished by a cushioning conversion machine, such as that disclosed in commonly assigned U.S. Pat. No. 5,123,889. The conversion machine disclosed in U.S. Pat. No. 5,123,889 converts sheet stock material, such as paper in multi-ply form, into relatively low density pads. Specifically, the machine converts this stock material into a continuous unconnected strip having lateral pillow portions separated by a thin central band. This strip is connected as by coining along its central band to form a coined strip which is cut into sections, or pads, of a desired length. The stock material preferably consists of three superimposed webs or layers of biodegradable, recyclable and reusable thirty-pound Kraft paper rolled onto a hollow cylindrical tube. A thirty-inch wide roll of this paper, which is approximately 450 feet long, weighs about 35 pounds and will provide cushioning equal to approximately sixty cubic feet of plastic foam peanuts while at the same time requiring less than one-thirtieth the storage space.
The conversion machines known in the prior art, including the one shown in U.S. Pat. No. 5,123,889, have used a freely rotating roll from which the stock material to be converted is fed by means of the same mechanism that advances the material through the forming portion of the machine. Specifically a pair of gears that have performed a connecting operation have been used to advance the material being converted. These gears stop and start their rotation during the conversion process, and this results in the need to accelerate the stock roll every time the gears start, with resulting changes in the tension of material being fed through the conversion machine. These changes in the tension of the material can affect the quality of the dunnage product being produced.
Also, when the conversion process is stopped, the rotational inertia of the stock roll can cause the stock roll to overrun and form a loose loop of material at the supply end of the conversion machine. When the conversion process is resumed, initially the material will be at a relatively low tension until the loose loop of material is taken up, at which point the tension on the paper will rapidly increase, almost instantaneously, to a relatively high level until the stock roll accelerates to match the feed rate through the machine. This quick change in tension can cause the material to tear, as well as degrade the quality of the dunnage product being produced.
The present invention provides a cushioning conversion machine and method for converting sheet stock material into a cushioning dunnage product and wherein the tension in the stock material is controlled to avoid one or more of the paper tension problems associated with prior art conversion machines and methods.
According to one aspect of the invention, a cushioning conversion machine and method for converting sheet stock material into a cushioning dunnage product are characterized by a stock supply assembly which supplies stock material to be converted, a conversion assembly which draws the stock material from the stock supply and converts the stock material into a strip of cushioning, and a controller which controls the operation of the conversion assembly. The conversion assembly is powered by a motor and the controller controls the operation of the motor in response to a sensed parameter related to the tension in the paper.
In one embodiment, a tension sensor is provided to sense the tension in the stock material as it is drawn from the stock supply by the conversion assembly and to provide to the controller an output signal indicative of the sensed tension. In response to the tension sensed by the tension sensor, the controller adjusts the speed of the motor thereby to adjust the rate at which the stock material is drawn from the stock supply to maintain a prescribed and preferably substantially constant tension in the stock material. In a preferred embodiment, the stock supply assembly includes a resiliently biased member over which the stock material is trained such that movement of the resiliently biased member is related to the tension in the stock material; and the tension sensor includes a sensing device which senses movement of the resiliently biased member against a biasing force and outputs a signal related to such movement of the resiliently biased member. A preferred resiliently biased member is an idler roller journalled in mounts at opposite ends of the idler roller, and a preferred sensing device includes load cells at the roller mounts. The output signals of the load cells at the roller mounts preferably are averaged to provide an averaged value of the measured tension in the stock material.
In another embodiment, motor torque is sensed and fed back to the controller as a measure of the tension in the stock material. In the case of an electric feed motor, motor current is sensed and fed back to the controller for maintaining the motor current in accordance with a prescribed criteria, such as below a predetermined maximum current.
According to another aspect of the invention, a cushioning conversion machine and method for converting sheet stock material into a cushioning dunnage product are characterized by a stock supply assembly which supplies stock material to be converted, and a conversion assembly which draws the stock material from the stock supply and converts the stock material into a strip of cushioning. The conversion assembly includes a feed mechanism which engages the stock material and feeds it through the conversion assembly. The feed mechanism is connected to a motor by a clutch device which limits the applied torque or force to the feed mechanism to a prescribed maximum value. In a preferred embodiment, a slip clutch is used to limit the torque applied by a motor to the feed mechanism which may include cooperating rotating feed wheels which not only feed the stock material but also function to connect together overlapped portions of the stock material.
Further in accordance with the invention, there is provided a method of converting sheet stock material into a cushioning dunnage product which includes drawing the stock material from a stock supply and converting the stock material into a strip of cushioning, while controlling the rate at which the stock material is drawn in response to the tension in the stock material.
The foregoing and other features of the invention are hereinafter fully described and particularly pointed out in the claims, the following description and the annexed drawings setting forth in detail one or more illustrative embodiments of the invention, such being indicative, however, of but one or a few of the various ways in which the principles of the invention may be employed.